Reviews : Java Books : Java and SOAP :

There is only one parameter for the executeTrade( ) method, an Object[] called params. The objects in this array must be cast to their corresponding types: a String, an Integer, and a Boolean. I like to put class casts inside a try/catch block in case the caller makes a mistake. That way I can do something useful if the method is called incorrectly, even if that means simply returning a description of the error. In Chapter 7, we'll look at generating SOAP faults for situations like this. The information passed in the array is used to generate a string that describes the parameters, and that string is stored in the result variable that is returned to the caller.

Now we can modify the client application so that it passes an appropriate Object[]as the parameter to the executeTrade service method. The multiParams variable is declared as an Object[], and is populated with the String MINDSTRM, an Integer with the value of 100, and a Boolean with the value of true. Since we're using an array of Java Object instances, we don't use Java primitives as elements of the array. Instead we wrap those primitive values in their Java object equivalents. The second parameter of the Parameter constructor is Object[].class, which is the class for an array of object instances.

package javasoap.book.ch5;
import java.net.*;
import java.util.*;
import org.apache.soap.*;
import org.apache.soap.rpc.*;
public class TradingClient {
   public static void main(String[] args) 
      throws Exception {
      
      URL url = 
        new URL(
          "http://georgetown:8080/soap/servlet/rpcrouter");
    
      Call call = new Call(  );
      call.setTargetObjectURI("urn:BasicTradingService");
      
      call.setEncodingStyleURI(Constants.NS_URI_SOAP_ENC);
      Object[] multiParams = { "MINDSTRM", new Integer(100), 
                                    new Boolean(true) };
      Vector params = new Vector(  );
      params.addElement(new Parameter("params", 
                           Object[].class, multiParams, null));
      call.setParams(params);
      
      try {
         call.setMethodName("executeTrade");
         Response resp = call.invoke(url, "");
         Parameter ret = resp.getReturnValue(  );
         Object value = ret.getValue(  );
         System.out.println("Trade Description: " + value);
      }
      catch (SOAPException e) {
         System.err.println("Caught SOAPException (" +
                         e.getFaultCode(  ) + "): " +
                         e.getMessage(  ));
      }
   }
}

If all goes well, the result of executing the executeTrade( ) service method is:

Trade Description: Buy 100 of MINDSTRM

We could force the service object down another path by changing the order of the parameters in the multiParams array. In this case, we would encounter a class cast exception, and the method would return an error string.

Here is the SOAP envelope for the proper invocation of the executeTrade( ) service method:

<SOAP-ENV:Envelope 
  xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/"   
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
  xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  
  <SOAP-ENV:Body>
    <ns1:executeTrade xmlns:ns1="urn:BasicTradingService" 
      SOAP-ENV:encodingStyle=
          "http://schemas.xmlsoap.org/soap/encoding/">
  
      <params  
          xmlns:ns2="http://schemas.xmlsoap.org/soap/encoding/" 
          xsi:type="ns2:Array" ns2:arrayType="xsd:anyType[3]">
        <item xsi:type="xsd:string">MINDSTRM</item>
        <item xsi:type="xsd:int">100</item>
        <item xsi:type="xsd:boolean">true</item>
      </params>
    </ns1:executeTrade>
  </SOAP-ENV:Body>
</SOAP-ENV:Envelope>

The params element is typed by assigning the xsi:type attribute the value of ns2:Array. The only difference from the homogeneous case is that every array element has a different value assigned to the ns2:arrayType attribute. The value xsd:anyType[3] indicates that the array contains 3 elements, each of which can be of any valid data type. [2]

Now let's take a look at passing arrays as parameters using GLUE. The BasicTradingService class can be deployed in GLUE without modification. We'll use a simple Java application to get this service started:

package javasoap.book.ch5;
import electric.util.Context;
import electric.registry.Registry;
import electric.server.http.HTTP;
public class BasicTradingApp {
   public static void main( String[] args )
      throws Exception {
    
      HTTP.startup("http://georgetown:8004/glue");
      Context context = new Context(  );
      context.addProperty("activation", "application");
      context.addProperty("namespace", 
                               "urn:BasicTradingService");
      Registry.publish("urn:BasicTradingService",
         javasoap.book.ch5.BasicTradingService.class, context );
   }
}

Compile and execute the application, and the service is deployed. Now let's write a simple example to access the service using the GLUE API. First let's look at the interface to the service, IBasicTradingService:

package javasoap.book.ch5;
public interface IBasicTradingService {
  int getTotalVolume(String[] symbols);
  String executeTrade(Object[] params);
}

2. In Chapter 3, we talked about using ur-type to represent any possible data type. Here we see the use of anyType for that purpose. The XML Schema Part 0 recommendation, dated May 2, 2001, explains this in section 2.5.4 as follows: "The anyType represents an abstraction called the ur-type which is the base type from which all simple and complex types are derived. An anyType type does not constrain its content in any way."

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